It's taken me a while to find a show worthy of my top accolade, but my first five stars of this year's Fringe go to... drumroll, please... A Stroke Of Genius. It's a funny-but-serious, visually striking and very slickly-presented play - which manages to tackle topics as big as genetics, identity and evolution, while staying fresh and fun.

The forgivably far-fetched plot centres on a rural librarian, Dora, who fears disaster when her beloved library shuts down. Confronted with the loss of her once-secure future, she sets her heart on a baby; and not just any baby, but a gifted one. And so Dora embarks on a complicated and murderous scheme, blackmailing an official, drugging an explorer, hoodwinking a scientist and, ultimately, impregnating herself with stolen sperm.

Initially I feared Dora was too much of a stereotype - and I stand by a suspicion that her socially-inept voice and manner are rather over-done. It didn't really matter, though; as you get to know her during the play, you'll see beyond the exterior, and the motivations for her wickedness prove quite touching in the end. Ali, the young scientist Dora exploits, is nicely drawn too - likeable and vulnerable, his role's to make you go "awww", and he carries it off to perfection.

But what sets this play apart is its innovative use of projected video. Let's face it, projection's old hat now - but A Stroke Of Genius literally casts it in a whole new light. There's a raft of memorable tricks to enjoy, such as opening a box to "reveal" a projected video inside. And, far from just a gimmick, light of all kinds is an important theme: towards the end it adopts an almost physical quality, as the sinister baddie Mr Product menaces the cowering Ali with a torch.

It's easy to overlook, but what enables all these visually arresting moments is the utterly flawless movement and timing. Every character and every prop is positioned in exactly the right beam of light, at exactly the moment the projector turns on. Some almost dance-like sequences bring the piece further to life, with desks, boxes and the other paraphernalia of the library pressed into use as a deliciously dynamic supporting cast.

The play avoids being too heavy-handed with its message, but there is a message there to be read. In one striking sequence, the actors step out of character to perform a chilling but compelling run-through of the history of eugenics. Thinking about it now, I realise it was a PowerPoint presentation shoe-horned into a play; in lesser hands it would have been annoying and preachy. But it was so slickly done that I accepted it without question - and I learned some startling historical facts along the way.

Innovative, thought-provoking and full of low-key humour, A Stroke Of Genius is what the Fringe is all about. I'll remember it for its tricks of the light and, even more, for its perfect execution on stage. And I'll remember it, too, for a fresh and unexpected plot - which kept me guessing right through to the final bombshell, dropped in, oh-so-quietly, at the very end.